Bingo, you it hit on the head...

He was just creating on his own. He was just engineering out of curiosity on what he found. There was no point to it. He was just experimenting, and I believe he intentional picked out Noomi's love interest to prove a point about creation and destruction, because Noomi firmly believed in god and spirituality. David firmly believed that creation is just creation, and everything evolves for the simple purpose of evolving and being experimental. ..DAvid didn't go around infecting everybody. he intentional selected one person.

( It's like scientists creating in the lab for the significance of generating something different, or to create something that has never been created before....but then destroying that creation because it has served its purpose, or because the concept or idea is an old model....THE ENGINEERS were no different, and I'm pretty sure they evolved from something, just like we evolved from primates, and computers and robots are evolving from us...David was trying to prove that to Noomi)

Also, one thing I want to point out which is incredible, remember when david was in the bio-engineering chamber, and he took samples of the black milky substance from the containers? There were no organisms inside the containers, but over time the substance morphed into something...It's like the weapon was some type of biological morphing substance that converted into an organism based on the DNA of the opposite subject, or the person it comes into contact with......Also, the small worms on the ground were the ones that changed into paranormal pythons within minutes of the scientist being in the room.

shit is wild.

My mind is all fucked up in a good way off of this movie..Thank you Ridley!!!!

Also,Also, remember Noomi's love interest transmogrified into some type of superhuman monster after being infected, and the organism that was inside of noomi morphed into an octopus version of the paranormal pythons that were in the chamber.....